AB1129 UTILITY OF LOW-DOSE COMPUTED TOMOGRAPHY (LDCT) FOR IDENTIFYING PATIENTS WITH AXIAL PSORIATIC ARTHRITIS (AXPSA) – A CROSS-SECTIONAL STUDY
Authors: I. T. Cheng, H. So, J. So, J. F. Griffith, L. S. Tam
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Psoriatic arthritis (PsA) is a multicentric disease with axial involvement being a critical feature. As inflammatory back pain (IBP) may be atypical or even absent, axial PsA is often under diagnosed. Axial PsA (axPsA) is currently diagnosed by identifying sacroiliitis on radiography. However, the detection of radiographic sacroiliitis is not entirely reliable and is challenging in early disease. Recently, magnetic resonance imaging (MRI) has been used to diagnose sacroiliitis to good effect. Even more recently, low dose (&lt;0.5mSv) computed tomography (LDCT) has been used to identify structural changes of sacroiliitis such as erosions and ankylosis. However, the usefulness of LDCT for diagnosing sacroiliitis in axPsA compared to radiography and MRI remains uncertain. <h3>Objectives</h3> To investigate the usefulness of LDCT in diagnosing axPsA-related sacroiliitis compared to radiography and MRI. <h3>Methods</h3> Consecutive biologic disease modifying anti-rheumatic drug (bDMARDs)-naïve patients who fulfilled CASPAR were recruited into this cross-sectional study, regardless of the presence of back pain. Radiographs of the pelvis, LDCT and MRI of the sacroiliac joints were performed. <h3>Results</h3> 33 patients (age: 45 ± 12 years, 23 (70%) male, disease duration: 3.0 ± 6.5 years) were recruited. The cohort had moderate peripheral joint disease (Disease Activity in Psoriatic Arthritis (DAPSA): 18.78 ±1 6.33) and skin disease (Psoriasis Area Severity Index (PASI): 5.40 ± 7.10). Axial disease activity (Ankylosing Spondylitis Disease Activity Score, ASDAS) was 2.52 ± 1.26. Twenty (61%) patients were on conventional synthetic DMARDs. Radiography revealed definite sacroiliitis according to modified New York criteria in 2 (6%) patients while 8 (24%) patients had possible sacroiliitis and 23 (70%) had no sacroiliitis. LDCT revealed sacroiliitis in 9 (27%) patients, including both patients with radiographic sacroiliitis, 7 (88%) of the 8 patients with possible radiographic sacroiliitis and 2 (4%) of 23 patients with normal radiographs (Figure 1). Patient with LDCT-sacroiliitis had longer symptom duration, higher patients' pain score, physician global, enthesitis scores and Bath Ankylosing Spondylitis Metrology Index (BASMI) (Table 1). The presence of human leukocyte antigen (HLA) B27, IBP, and fulfillment of the Assessment of SpondyloArthritis international Society (ASAS) 2009 criteria of axial spondylitis could not differentiate between patients with or without LDCT-sacroiliitis. LDCT had 100% agreement with MRI. MRI detected 9 patients with sacroiliitis, all of whom were identified by LDCT. <h3>Conclusion</h3> LCDT revealed sacroiliitis in 4 times more patients than radiographs. Patients with sacroiliitis had higher disease activity across various disease domains. LDCT had excellent agreement with MRI. LDCT is very helpful for diagnosing axPsA, especially when access to MRI is limited. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.